1. Field of the Invention
The present invention relates to a method and apparatus for enabling cold temperature performance of a disk.
2. Background of the Invention
There are environmental conditions where applying power and attempting to spin up a magnetic disk drive storage device can lead to extensive and often irreversible damage and data loss. Among such detrimental environmental conditions is cold temperatures. Manufacturers often warn users of computer systems, particularly personal computers and laptop computers, to avoid turning on xe2x80x9ccoldxe2x80x9d or xe2x80x9cfrozenxe2x80x9d systems until the unit has warmed up to a xe2x80x9csafexe2x80x9d temperature. Unfortunately, such warnings are often unheeded, or completely ignored, by users. Thus, it is imperative to protect such computer systems from damage and/or data loss resulting from such ill-advised attempts at turning on xe2x80x9ccoldxe2x80x9d or xe2x80x9cfrozenxe2x80x9d systems before the unit has been sufficiently warmed up.
Direct access storage devices, or hard drives, are widely used in modern computers. Disk drive units, often incorporating stacked, commonly rotated rigid magnetic disks for example, are used for storage of data in magnetic form on the disk surfaces. Data may be recorded in radially spaced data information tracked arrays on the surfaces of the disks. Transducer heads driven in a path towards and away from the drive axis write data to the disks and read data from the disks.
FIG. 2 shows an example of a data storage disk file 100 that includes a magnetic disk drive unit 102 and interface control unit 114. Magnetic disk drive unit 102 includes at least one disk 116 having at least one magnetic surface 118 which may be contained within a disk drive enclosure 122. The disk 116 may be mounted for rotation on and by integrated spindle motor assembly 126. Information on each magnetic disk surface 118 may be read from or written to the disk surface 118 by a corresponding transducer head assembly 128 which may be movable in a path having a radial component across the rotating disk surface 118. Each transducer head assembly 128 may be carried by a suspension arm assembly 130. The suspension arm assemblies 130 are bundled together for simultaneous pivotal movement by actuator coil motor 132 cooperating with an internal magnet and core assembly. Drive signals applied to the actuator coil motor 132 cause the suspension arm assemblies 130 to move in unison to position the transducer head assemblies 128 in correspondence with information storage tracks on the disk surfaces 118 on which information may be written or read.
In particular, disk drive unit 102 has two major mechanical mechanisms that may be affected by cold temperatures. The first mechanism is actuator coil motor 132, where read/write heads are disposed, and the second mechanism is spindle motor assembly 126. The problem that cold weather poses to the spindle motor assembly 126 is that, since a torque constant increases as the temperature thereof decreases, grease in the bearings thereof becomes more viscous thereby affecting the performance and ability to move or spin the disk drive.
Current solutions for operation of disk drive unit 102 in cold temperatures include attaching a resistive heater to the top cover 122 of the disk drive unit 102, wherein the heater may be a resistive wire encapsulated in captan sheet. A thermistor, or equivalent temperature sensor, may then attached to the disk drive unit 102 or adjacent thereto to thereby measure ambient temperature. During system power up, the temperature of the disk drive unit 102 is measured before spin-up of the actuator coil motor 132 or spindle motor assembly 126. If the measured temperature is below a predetermined minimum threshold temperature, current (either DC, AC or pulsed current) may be applied to the heater, and the temperature may be measured once more. The steps described above are repeated as necessary until the measured temperature equals or exceeds the minimum threshold temperature. Then the heater may be turned off, and power may be applied to the disk drive unit 102. The actuator coil motor 132 and spindle motor assembly 126, while spinning and read/write accessing, should then provide sufficient heat dissipation to self-heat the disk drive. However, if the temperature of the disk drive unit 102 drops below a set-limit (i.e., 10xc2x0 C. below the minimum threshold temperature for example), then the heater may once again be turned on until temperature of the disk drive unit 102 equals or exceeds the minimum threshold temperature. This method requires a significant amount of power to completely heat up the entire disk drive unit 102 prior to spin up of both the actuator coil motor 132 and the spindle motor assembly 126.
Thus, it is essential to overcome the problems posed by cold weather environments on the normal operation of hard disk drives, which until present has been done by merely avoiding turning on xe2x80x9ccoldxe2x80x9d or xe2x80x9cfrozenxe2x80x9d systems until the unit has warmed up to a xe2x80x9csafexe2x80x9d temperature. Since such warnings are often unheeded, or completely ignored, by users, it is imperative to protect such computer systems from damage and/or data loss resulting from such ill-advised attempts at turning on xe2x80x9ccoldxe2x80x9d or xe2x80x9cfrozenxe2x80x9d systems before the unit has been sufficiently warmed up.
It is, therefore, a principle of object of this invention to provide a method and apparatus for enabling cold temperature performance of a disk.
It is another object of the invention to provide a method and apparatus for enabling cold temperature performance of a disk that solves the above-mentioned problems.
These and other objects of the present invention are accomplished by the method and apparatus for enabling cold temperature performance of a disk disclosed herein.
In view of the fact that spindle torque requirements increase as a temperature thereof decreases, the present invention overcomes the higher torque required due to the increased viscosity of the grease by localizing the heating to the spindle motor assembly. Thus, the viscosity of the grease is reduced, and therefore the present invention enables self-heating by the disk drive during and after spin-up of the spindle motor assembly.
According to a first example embodiment of the present invention a small current (DC, AC or pulsed current) may be applied to one or more windings of a stator of a disk drive unit. Due to the electrical resistance within the windings, heat may be dissipated in the spindle motor assembly, and the dissipated heat may be conducted into the bearing and bearing grease. The grease may then warm to a minimum threshold temperature, thus providing a safe environment for normal operation of spindle motor assembly.
The amount of time required for the current, including any one of a constant DC current AC current and pulsed current, to be applied to the windings of the stator of the disk drive unit may be determined utilizing one of the following. First, in consideration of a voltage measurement of the spindle motor assembly, experimental measurements may be made on spindle motor assembly to determine the change in the resistance of the windings as they change with temperature depending on the change in current or voltage on a given winding. Such measurements may be stored in a table within a controller of the disk drive unit and once the given resistance value is obtained, normal spinning operation of spindle motor assembly may commence.
Secondly, a thermistor may be provided on a card of the disk drive unit. The controller first determines the disk drive card temperature prior to power up. If the temperature disk drive unit card is less than the minimum threshold temperature, the controller performs a table look up for the temperature that is closest to the measured temperature. The controller then applies a current to the stator windings for the given time as specified within the table prior to spin-up of the spindle motor assembly.
The spin-up times would be experimentally determined for each motor by measuring the bearing temperature versus time of current injection into the winding(s) of the spindle motor stator.
Lastly, a closed loop feedback to the controller may be provided for the heating cycle. The thermistor attached to the spindle motor would be polled when initial power is applied to the disk drive unit. If the measured temperature is less than the minimum threshold temperature, the controller may apply a current, including any one of a DC, AC or pulsed current, to the spindle motor windings, and then continuously monitor the thermistor temperature until the threshold minimum thermistor temperature has been achieved to thereby enable normal spin-up of the spindle motor assembly.
A second example embodiment of the present invention is similar to the first example embodiment described above except that, instead of applying a current, including any one of a DC, AC or pulsed current, the phases of spindle motor assembly are excited to rock the spindle motor assembly in a xe2x80x9cback-and-forthxe2x80x9d manner, while avoiding spindle fretting, such that heat is dissipated within the windings and, as a result, heat may be dissipated into the grease. The amount of time that the phases are rocked to generate heat to be dissipated within the windings may be determined by the exemplary methodologies described above.
A third example embodiment of the present invention directly applies a heater to the outside of the spindle motor assembly, or may be alternatively integrated within spindle motor assembly, adjacent to the bearing assembly. The heater and thermistor may be cabled within the same cable bundle as the multiple phases and neutral, and would be focused to heat only the spindle motor assembly as quickly and efficiently as possible.